Embodiments relate generally to magnetic devices, and in particular to a magnetic assembly formed on a printed circuit board.
Magnetic devices come in a variety of forms. For example, uncut toroidal-core wound magnetic devices (transformers, inductors, saturable reactors) are typically wire wound by either hand or mechanical means utilizing a wire shuttle. These assemblies are then self-leaded, potted, or mounted in carriers. These higher level assemblies are then integrated into the intended application.
Alternatively, magnetic devices can be based on separable magnetic structures. These include “E”, “U”, “cut toroid”, “tape-wound”, and “pot” cores or laminations. These structures typically use bobbins or coil formers. The copper wire is wound on the bobbin, and the core pieces are assembled around the bobbin and/or winding(s). Printed circuit boards can also be assembled within windows in the structure to form windings.
Both separable core geometries and carrier-mounted toroid assemblies require their bobbins or carriers and/or leads to bear the mass of the entire assembly. Therefore in rugged applications, the printed circuit pads and traces, the bobbin, the self-leads, and/or the solder joints are critical failure locations. Common failure modes for these joints include printed circuit board tearing/delamination and solder joint cracking through tension and bending. Leads may also be bent and torn.
The winding window of an uncut toroid core is geometrically and permanently closed. Therefore, in assembly, the conductor must be repeatedly passed through the winding window. This requires working with long pre-cut lengths of conductor, special winding machines, work-hardening of the conductor, post-assembly annealing of conductor material through heat treating processes. All of the above assembly steps add time and cost to the finished assembly.
Most copper losses are conducted through the electrical contacts of alternative magnetic device assemblies. In typical arrangements, heat is only transferred through convection (natural or forced air), or via conduction through thermally-conductive properties of electrical insulator materials (bobbins, varnishes, potting compounds). Direct conduction of heat from magnetic cores can be accomplished in some geometries. Dissipating the heat generated by the core and windings of a magnetic device strictly through convection or conduction through electrical insulator materials is inefficient, and can lead to excessive internal temperatures and thermal gradients throughout the device. Separable core geometries employing a localized air-gap have localized heat dissipation, which makes them undesirable in high-temperature, high-reliability applications.
There is a need in the art for a rugged magnetic assembly having improved heat dissipation.